Ion beam apparatus and method employing magnetic scanning

ABSTRACT

A multipurpose ion implanter beam line configuration comprising a mass analyzer magnet followed by a magnetic scanner and magnetic collimator combination that introduce bends to the beam path, the beam line constructed for enabling implantation of common monatomic dopant ion species cluster ions, the beam line configuration having a mass analyzer magnet defining a pole gap of substantial width between ferromagnetic poles of the magnet and a mass selection aperture, the analyzer magnet sized to accept an ion beam from a slot-form ion source extraction aperture of at least about 80 mm height and at least about 7 mm width, and to produce dispersion at the mass selection aperture in a plane corresponding to the width of the beam, the mass selection aperture capable of being set to a mass-selection width sized to select a beam of the cluster ions of the same dopant species but incrementally differing molecular weights, the mass selection aperture also capable of being set to a substantially narrower mass-selection width and the analyzer magnet having a resolution at the selection aperture sufficient to enable selection of a beam of monatomic dopant ions of substantially a single atomic or molecular weight, the magnetic scanner and magnetic collimator being constructed to successively bend the ion beam in the same sense, which is in the opposite sense to that of the bend introduced by the analyzer magnet of the beam line.

The field of invention relates to ion implanting into semiconductorwafers and other substrate targets. It relates in particular toefficiently implanting molecular ions which contain multiple atoms of anelectrical dopant species such as the elements B, P, As, Sb, and Inwhich lie in the periodic table on either side of the group IV elementsof C, Si, Ge, and Sn, and also for efficiently implanting molecular ionswhich contain multiple atoms of elements such as C, Si, or Ge which arenow being used for modifying the semiconductor substrate to effectuate,for example, amorphization, dopant diffusion control, stressengineering, or defect gettering. Such molecular implants, particularlythose with ions having a large multiplicity of atoms of interest, i.e. 4or more, are useful for fabricating integrated circuits with criticaldimensions of 60 nm and less. The field of invention also relates toimplanter beam line configurations that are also suitable for thecommonly used single atom dopant ions, and especially to multipurposeimplanter beam line configurations useful for implanting all threeclasses of the aforementioned ions.

BACKGROUND

For the case of high dose, low energy implants, the potential advantageof using molecular ions containing multiple atoms of elements ofinterest has been well recognized for several years. For a given ionbeam current the dose is increased in proportion to the atomicmultiplicity of the element of interest. Such ions can be extracted froma source and transported to the wafer or other target substrate at amuch higher energy, in proportion to the ratio of the molecular mass tothe atomic mass of the element of interest. Consequently, for relativelyhigh dose implants, the wafer throughput is not as seriously limited bythe internal space charge forces and the intrinsic thermal iontemperature within the ion beam. Also, for a given dose, the electricalcharge delivered to the wafer by the beam is substantially less.

However, it is desirable to overcome a number of drawbacks that existwhen an attempt is made to use such molecular ions in a conventionalimplanter. Firstly, the ion source of a conventional ion implanter has arelatively high density, hot plasma and heavy molecular ions aresubstantially disintegrated by such a source, often resulting in a lowmolecular ion yield. Secondly, the molecular ions are often generatedwith a range of masses as a result of various amounts of hydrogen atomswithin the ion and also as a result of the binomial distribution ofisotopic masses if there is more than one isotope of an element presentin the generated ions. The different mass ions generally describedifferent paths through the implanter beam line and as a result canproduce undesirable angular and/or dose variations over the surface of awafer. Thirdly, the relatively high mass of the molecular ions limitsthe single atom implant energy, often to just a few keV because of thelimited field strength and size of the conventional analyzer magnet (andother magnetic elements if used).

To minimize the commercial costs associated with constructing andoperating an ion implanter tool, it is also desired to have an ionimplanter that is multipurpose, capable not only of overcoming thedrawbacks associated with implanting the molecular ions, but alsocapable of implanting common monatomic dopant species.

Furthermore, it is desirable, even with ion implanters that areconstructed principally for implanting common monatomic dopant species,to enable efficient operation over a wide range of ion densities in thebeam in order to meet the large dynamic range of doses generallyrequired, to provide high ion purity at the target with respect to theion energy resolution and with respect to freedom from ion species whichwould degrade the semiconductor structures, and to impinge ions on tothe wafer substrate with a small angular spread, good angulardefinition, and good dose uniformity over the surface of the wafer.

SUMMARY

According to one aspect of invention a multipurpose ion implanter beamline configuration comprises a mass analyzer magnet followed by amagnetic scanner and magnetic collimator combination that introducebends to the beam path, the beam line constructed for enablingimplantation of common monatomic dopant ion species cluster ions, thebeam line configuration having a mass analyzer magnet defining a polegap of substantial width between ferromagnetic poles of the magnet and amass selection aperture, the analyzer magnet sized to accept an ion beamfrom a slot-form ion source extraction aperture of at least about 80 mmheight and at least about 7 mm width, and to produce dispersion at themass selection aperture in a plane corresponding to the width of thebeam, the mass selection aperture capable of being set to amass-selection width sized to select a beam of the cluster ions of thesame dopant species but incrementally differing molecular weights, themass selection aperture also capable of being set to a substantiallynarrower mass-selection width and the analyzer magnet having aresolution at the mass selection aperture sufficient to enable selectionof a beam of monatomic dopant ions of substantially a single atomic ormolecular weight, the magnetic scanner and magnetic collimator beingconstructed to successively bend the ion beam in the same sense, whichis in the opposite sense to that of the bend introduced by the analyzermagnet of the beam line.

Implementations of this aspect of invention may have one or more of thefollowing features.

The mass selection aperture is capable of being set to a first settingfor monatomic ion species and a second setting of at least fifteen timesthe mass-selection width of the first setting for accepting cluster ionsgenerated from boron-containing compounds. The resolution of the massanalyzer magnet at the mass selection aperture for monatomic doping ionsis at least 60. The mass analyzer magnet is sized constructed andarranged to form at the mass selection aperture a conjugate image in themass dispersive plane of the width of the ion source extractionaperture. The mass selection aperture of the analyzer magnet is capableof being set to an aperture width of at least 30 mm. The analyzer magnetis constructed to analyze a beam extracted from a slot-form ion sourceextraction aperture of at least 12 mm width and 90 mm height. The massselection aperture is capable of being set to a first setting for themonatomic ion species and to a second setting of at least fifteen timesthe mass-selection width of the first setting for accepting cluster ionsof multiple masses near a peak of interest, and the resolution of themass analyzer magnet at the mass selection aperture for monatomic dopingions is at least 60. The slot-form extraction aperture width is about12.5 mm and height about 100 mm. The ion implanter beam line is providedin combination with an ion source constructed to produce ions of currentdensity up to about 1 mA/cm² by an ionization mode employing a formedelectron beam, the ion source constructed to receive feed materialalternatively in the forms of gas and heated vapor. The ion source isconstructed to function alternatively in a second ionization modeemploying arc discharge. The analyzer magnet is a sector magnetconstructed to produce an adjustable magnetic field in the pole gapincluding a field exceeding about 10 kGauss. The ion implanter beam lineis constructed to select about 80 keV ions generated fromoctadecaborane. The mass analyzer comprises a sector magnet having aradius R of about 500 mm, a sector angle Φ of about 120 degrees, adistance b from the pole exit to the mass resolving aperture of about195 mm, the mass analyzer having a magnification M of about −0.83, theanalyzer magnet constructed to analyze an ion beam from a source havingan extraction aperture width of about 12.5 mm, the analyzer magnethaving mass resolution m/Δm of the order of about 88. The ion implanterbeam line includes a multiple element quadrupole focusing lens in theportion of the beam line following the analyzer magnet, the lensarranged to control the dimensions of the beam in orthogonal directionsof the beam cross-section. The lens has at least three quadrupoleelements and is constructed to simultaneously control the dimensions andangular divergence of the beam in orthogonal directions of the beamcross-section. The lens is a quadrupole triplet focusing lens. The lensis a magnetic quadrupole triplet focusing lens. The ion implanter beamline is constructed to produce a beam having an elongated cross-sectionprofile entering the quadrupole triplet focusing lens, with the longdimension of the beam profile in the plane normal to the plane of thebend of the analyzer magnet, in combination with a control adapted tocause the first lens element of the triplet to cause focusing in thelong profile dimension, the second lens element to have polarityopposite to that of the first element to cause focusing in the shortdimension and defocusing in the long dimension, and the third lenselement to have the same polarity as the first element, field strengthsof the lens elements controlled, respectively, to achieve simultaneousfocusing in both dimensions of the elongated profile. The ion implanterbeam line includes a decelerating unit following the analyzer magnet andpreceding the quadrupole lens, the lens controlled to control beamdivergence resulting from deceleration of the beam at the deceleratingunit. The ion implanter beam line has beam line features and parametersof substantially the following values;

-   -   A. Analyzer Magnet: R=500 mm, φ=120°; G=118 mm; s₁=31 mm; s₂=8.6        mm; h₁=8.7 mm; h₂=4.7 mm; W=166 mm; bending power=80 keV        octadecaborane.    -   B. Mass selection aperture: about 8 mm minimum to about 38 mm        maximum.    -   C. Quadrupole triplet focusing lens: aperture: 80 diagonal        between pole tips; pole tip field adjustable 0-5 kGauss.    -   D. Beam Scanning Magnet; Vertical gap=80 mm; bending power=80        keV octadecaborane.    -   E. Collimator: Bending radius 900 mm; Pole gap=8 mm; bending        power=80 keV octadecaborane and the total deflection introduced        by the scanner and collimator combination being about 30°.

Another aspect of the invention is an ion implanter beam lineconfiguration constructed for enabling implantation of cluster ions, thebeam line configuration comprising a mass analyzer magnet followed by amagnetic scanner and magnetic collimator combination that introducebends to the beam path, the mass analyzer magnet defining a pole gapbetween ferromagnetic poles of the magnet and a mass selection aperture,the pole gap sized to accept an ion beam from a low density ion sourcethat produces the cluster ions, the mass selection aperture capable ofbeing set to a mass-selection width sized to select a beam of thecluster ions of the same dopant species but incrementally differingmolecular weights, the ion implanter beam line including a multi-elementfocusing system in the portion of the beam line following the analyzermagnet which comprises multiple quadrupole focusing elements, theindividual field strengths of the lens elements of the lens systemadjusted to control the dimensions of the beam in orthogonal directionsof the beam cross-section and to simultaneously and substantially removeangular deviation at the target substrate that otherwise would occur asa result of the range of different masses of the cluster ions in the ionbeam the magnetic scanner and magnetic collimator being constructed tosuccessively bend the ion beam in the same sense, which is in theopposite sense to that of the bend introduced by the analyzer magnet ofthe beam line.

Implementations of this aspect of invention may have one or more of thefollowing features.

The lens system has at least three quadrupole elements and isconstructed to simultaneously control the dimensions and angulardivergence of the beam in orthogonal directions of the beamcross-section by quadrupole fields. The lens system is a quadrupoletriplet focusing lens. The lens is a magnetic quadrupole tripletfocusing lens. The ion implanter beam line is constructed to produce abeam with an elongated cross-section profile entering the quadrupoletriplet focusing lens, with the long dimension of the beam profile inthe plane normal to the plane of the bend of the analyzer magnet, incombination with a control adapted to cause the first lens element ofthe triplet to cause focusing in the long profile dimension, the secondlens element to have polarity opposite to that of the first element tocause focusing in the short dimension and defocusing in the longdimension, and the third lens element to have the same polarity as thefirst element, field strengths of the lens elements controlled,respectively, to achieve simultaneous focusing in both dimensions of theelongated profile. The ion implanter beam line includes a deceleratingunit following the analyzer magnet and preceding the quadrupole lenssystem in the form of a quadrupole triplet lens, the quadrupole lenssystem controlled to control beam divergence resulting from decelerationof the beam at the decelerating unit.

Another aspect of invention is an ion implantation beam line for usewith an ion source, the beam line comprising a mass analyzer magnetfollowed by a magnet scanner and magnetic collimator combination thatintroduce bends to the beam path, the analyzer magnet for an ionimplanter beam line comprising a sector magnet having a center pathradius of about 500 mm, a sector angle of about 120° and a pole gap ofat least about 80 mm, the magnet associated with a single pair of coils,the magnet having entrance and exit pole faces perpendicular to the axisof the ion beam path entering and leaving the pole gap, the analyzermagnet having substantially no focusing effect upon the beam in theplane perpendicular to the plane of bend of the sector magnet, themagnetic scanner and magnetic collimator being constructed tosuccessively bend the ion beam in the same sense, which is in theopposite sense to that of the bend introduced by the analyzer magnet ofthe beam line.

Implementations of this aspect of invention may have one or more of thefollowing features.

The ion implantation beam is in combination with an ion focusing systempreceding the magnet providing beam focusing in the plane perpendicularto the mass-dispersive plane of the magnet. The focusing systemcomprises lens elements of an ion extraction system associated with theion source. The pole gap of the analyzer magnet is substantially widerthan the corresponding dimension of the maximum size ion beam it isconstructed to pass, there being a lining of graphite or silicon betweenfaces of the poles and the beam path. Pole members of the analyzermagnet defining the pole gap have pole faces shaped with trenches andshims that respectively lower and raise the pole surfaces toward themedian plane of the beam path to shape the magnetic field in mannerenabling use of relatively small pole width in relation to the pole gapdimension. Pole members defining the pole gap are embedded in and sealedto the wall of a vacuum housing of nonmagnetic material through whichthe ion beam passes while subjected to the magnetic field of theanalyzer magnet, and ferromagnetic structure of the magnet between thepole members being located outside of the vacuum housing. The analyzermagnet is a sector magnet constructed to produce an adjustable magneticfield in the pole gap including a field exceeding about 10 kGauss. Theanalyzer magnet is constructed to analyze a beam extracted from aslot-form ion source extraction aperture of at least 12 mm width and 90mm height.

The details of one or more embodiments of the foregoing aspects andfeatures are set forth in the accompanying drawings and the descriptionbelow. Other features, objects, and advantages of the invention will beapparent from the description and drawings, and from the claims.

DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic illustration of an ion implanter employing asector mass analyzing magnet.

FIG. 2 is a cross-sectional view through the magnetic analyzer of FIG. 1along section lines A-A and B-B.

FIG. 3 is an enlarged view of the decelerator shown in FIG. 1.

FIG. 4 is a cross section of the high voltage isolated coil of theanalyzer magnet.

FIG. 5 is an enlarged view of a portion of the coil cross-section shownFIG. 4.

FIG. 6 is a schematic illustration showing ion paths of different mass.

FIG. 7 shows the variation of dispersion (D/R) with bending angle.

FIGS. 8A and 8B shows a cross-sectional view of an analyzer pole shapewhile FIG. 8C is a magnified detail of the mounting of a pole.

FIG. 9 show a high resolution mass spectrum of octadecaborane.

FIGS. 10A-D shows an adjustable mass resolving aperture apparatus.

FIG. 11 shows the beam envelope in the horizontal plane in the region ofthe ion source.

FIGS. 12A and B show a magnetic quadrupole triplet in longitudinal andtransverse cross-section, respectively.

FIG. 13 shows a perspective view of a median plane cross-section of amagnetic scanning-beam line.

FIG. 14 is a diagrammatic vertical cross-section in the plane of anextracted ion beam, of an ion source useful in the embodiments of FIGS.1 and 13.

FIG. 14A is a diagrammatic example of other useful electrode shapes ofan ion source useful in the embodiments of FIGS. 1 and 13.

FIGS. 15A and 15B show an ion extraction system associated with the ionsource of FIG. 14, respectively in the dispersive and non-dispersiveplanes of the beam line.

FIGS. 16A and 16B show the ion beam envelope through the quadrupoletriplet of FIGS. 12A and 12B, respectively in the dispersive andnon-dispersive planes of the beam line.

FIG. 17 is a plot of particle boron beam current against implant energymeasured during operation of a system corresponding to FIG. 13.

FIG. 17A are plots of the particle boron beam current against implantenergy using SF₆ and deceleration.

FIG. 18 is a view similar to that of FIG. 14 of a dual mode ion source.

FIG. 19 is a schematic illustration of a beam-line for a medium currentimplanter.

DETAILED DESCRIPTION

Referring now to the drawings, wherein identical parts are referenced byidentical reference numerals and functionally similar parts by identicalreference accented numerals, FIG. 1 schematically illustrates oneembodiment of an ion implanter beam-line useful for efficientlyimplanting molecular ions which contain multiple atoms of an electricaldopant species such as the elements B, P, As, Sb, and In which lie inthe periodic table on either side of the group IV elements of C, Si, Ge,and Sn, and also for efficiently implanting molecular ions which containmultiple atoms of elements such as C, Si, or Ge useful for modifying asemiconductor substrate to effectuate, for example, amorphization,dopant diffusion control, stress engineering, or defect gettering. Suchmolecular ions can be useful for fabricating integrated circuits withcritical dimensions of 60 nm and less. Hereinafter, such ions will becollectively referred to as “cluster” ions.

The chemical composition of a singly charged cluster ion has the generalform

M_(m)D_(n)R_(x)H_(y) ⁺  (1)

where M is an atom such as C, Si, or Ge useful for material modificationof the substrate; D is a doping atom such as B, P, As, Sb, or In (fromgroup III or IV of the Periodic Table) for implanting a charge carrierin to the substrate; R is a radical, ligand, or molecule; and H is ahydrogen atom. Generally, R or H are present simply as part of thecomplete chemical structure needed to produce or form a stable ion andare not specifically required for the implant process. In general H isnot significantly detrimental to the implant process. The same should betrue for R. For example it would be undesirable for R to contain ametallic atom such as Fe, or an atom such as Br. In the above equationin, n, x, and y are all integers greater than or equal to zero, with thesum of m and n greater than or equal to two, i.e., m+n≧2. Of particularinterest in ion implantation are cluster ions with a high M and/or Datomic multiplicity, i.e those with m+n≧4, because of their improvedefficiency for low energy, high dose implants.

Examples of cluster ions that can be used for material modification arethose derived from adjoining benzene rings such as C₇H_(y) ⁺, C₁₄H_(y)⁺, C₁₆H_(y) ⁺, and C₁₈H_(y) ⁺. Examples of cluster ions that can be usedfor doping are

-   -   Borohydride ions: B₁₈H_(y) ⁺, B₁₀H_(y) ⁺.    -   Carborane ions: C₂B₁₀H_(y) ⁺ and C₄B₁₈H_(y) ⁺    -   Phosphorus hydride ions: P₇H_(y) ⁺, P₅(SiH₃)₅ ⁺, P₇(SiCH₃)₃ ⁺.    -   Arsenic hydride ions: As₅(SiH₃)₅ ⁺, As₇(SiCH₃)₃ ⁺.

One of ordinary skill in the art can appreciate the possibility of usingcluster ions other than those listed in the examples above, including:ions containing Si and Ge for material modification, ions with differentamounts and different isotopes of dopant atoms, and ions with differentisomeric structures. Doubly charged cluster ions are also generallyformed with a much smaller yield in which case they are not as usefulfor high dose, low energy implantation.

The field of invention also relates to implanter beam lineconfigurations that are also suitable for the commonly used single atomdopant ions, and especially to multi-purpose implanter beam lineconfigurations useful for implanting all three classes of aforementionedions.

Ions are extracted from an ion source chamber 10 inside an ion sourcebody 11 through an aperture 12 by an accelerating electric voltage(V_(e)) 13, typically in the range of 1 kV to 80 kV, applied between anextraction electrode 14 and the ion source chamber 10. Back-streamingelectrons are suppressed by applying to extraction electrode 14 avoltage (V_(s)) 9 of 2-10 kV negative with respect to the ion sourcevacuum housing 15 and suppressor electrode 7 via an insulatedfeed-through 8. The suppressor electrode 7 is at the same potential asthe ion source vacuum housing 15. The ion source body 11 is insulatedfrom the ion source vacuum housing 15 by an annular insulator 16. In oneuseful commercial embodiment the aperture 12 is slot shaped with a widthof w_(s)=12.5 mm and a height of h_(s)=100 mm. Such an aperture width islarger than the range of between about 3-5 mm typically used in ionsources commonly used for producing conventional ions such as B⁺, P⁺,As⁺, BF₂ ⁺ etc. The purpose of a large ion source aperture width andheight, providing a total area of 125 mm², is to provide a large areafrom which to extract cluster ions. This is because for one type ofsource useful for generating cluster ions (see FIG. 14-16B and relateddescription) the density of the ions is low within the chamber 10because the ion source uses a formed electron beam rather than a highdensity plasma to ionize the vapor from which the cluster ions areproduced. For example, such a type of ion sources are able to produceborohydride ions without significantly decomposing the borohydride vaporin the source, and, with the aperture 12 being of large size, producehigh borohydride ion currents that can meet the present day importantcommercial wafer throughput requirements for the very high dose dualpolygate structures and the medium dose but very low energy boron sourcedrain extension implants.

A vacuum of typically between about 10⁻⁶-10⁻⁴ torr is maintained in theion source vacuum 15 housing by a vacuum pump 17. Referring to FIG. 11,the electric field generated between the extraction electrode 14 and theion source body 11 and aperture 12 forms an approximately mono-energeticribbon shaped beam of ions 19 with a height dimension similar to that ofthe ion source aperture height h_(s), and a minimum width w_(b) (56)approximately equal to half the width w_(s) (5) of the ion sourceaperture 12, i.e. w_(b)˜0.5w_(s). This width w_(b) is located in theregion 59 of the ion source aperture 12 and extraction electrode 14. Thespacing d (57) between the ion source aperture and extraction electrodeis generally adjusted to optimize the extraction and beam formation fora given ion species, ion energy, ion mass, and ion beam current.

After extraction from the ion source 11, the beam 19 passes into avacuum housing 20 and then enters the magnetic field gap G of a dipolemagnet 21, (FIGS. 1 and 2) in which the beam envelope becomes oval-like.Magnet 21 is comprised of current carrying coils 40, and the followingferromagnetic component parts: poles 26, cores 28, yoke cheeks 30, yokereturns 32 and 34. Referring, in particular to FIG. 2, passing DCelectric current through the coil assemblies 40 generates a staticmagnetic field 24 generally in the vertical direction in the gap betweenthe poles 26 where “vertical” is defined as the direction of the longdirection of the source aperture 12 and for the embodiment shown inFIGS. 1 and 2 this direction is orthogonal to the generally “horizontal”bending (dispersive) plane of magnet 21.

The gas discharge from the ion source 11 is removed by a vacuum pump 17located on the ion source housing. The vacuum pump has sufficientcapacity (e.g. 1000-2000 liters/sec) to maintain a vacuum pressure inthe ion source housing 15 of between about 10⁻⁶-3×10⁻⁵ torr. Formaintenance ease of the ion source 10, 11, the ion source housing 15 isisolatable from the magnet vacuum housing 20 with a vacuum valve 23. Themagnet housing 20 is of non-ferromagnetic material (e.g. aluminum) toprevent magnetic interaction with the magnet body. It is evacuated byvacuum pump 29.

The radial force generated by the magnetic field 24, acting on theelectrical charge of the ions, causes the ions to describe substantiallycircular paths 42, 43, and 44 in the horizontal bending plane of themagnet 21. Since the ions extracted from the ion source chamber 10 allhave approximately the same energy, magnet 21 spatially separates thetrajectories of ions 43 and 44 that possess respectively higher andlower mass than ions 42 which travel along the center path 46 in themagnet pole gap. By constructing the magnet suitably large the magneticfield 24 can be set in the range from less than one kGauss to about 12kGauss and the magnetic field can be adjusted over a wide range ofmasses to select a given mass corresponding to ions 42 following thecenter path 46. In one embodiment the center path 46 has a radius ofapproximately 500 mm in which case at a field of approximately 12 kGaussthe magnetic analyzer is able to select 80 keV ions generated fromoctadecaborane (B₁₈H₂₂) vapor corresponding to a 4 keV boron implantenergy, which is typically the highest energy needed for present daydual polygate doping. Likewise, it is able to select 80 KeV ionsgenerated from decaborane (B₁₀H₁₄) vapor corresponding to a 7 KeV boronimplant energy.

Referring to FIGS. 1 and 11, the paths of ions 42 emerging from theextraction electrode 14 generally have a range of angles in thehorizontal plane from between about −50 milliradians to +50 milliradianswith respect to the central reference path 46 attributable to suchfactors as thermal motion of the ions at the point of their origin inthe ion source chamber 10 and the coloumb forces acting between ions oflike charge. In one embodiment the shape of the pole 26 generates amagnetic field 24 in the gap that causes the ion paths of a selectedmass to re-converge in the horizontal plane towards a slit-form massresolving aperture 50 at the exit of the magnet to enable massselection. An important aspect of the present embodiments of themagnetic analyzer 21 is that this mass selection aperture 50 is locatedat a point along the beam path which is near the ion optically conjugateimage of the aperture width 12 with respect to transverse, horizontalion motion. The optical magnification M of the conjugate image istypically between about −0.8 to −1.2, the negative sign implying theformation of a real inverted image. If the width of the mass resolvingslit 50 is set to a value w_(r) equal to the product of the ion beamwaist width w_(b)˜0.5w_(s) and the magnification M, i.e.

w_(r)˜0.5|M|w_(s)  (1)

then most of the ions 42 of a selected mass m, emerging from ion source11 within a horizontal angle between about −50 milliradians to +50milliradians, will be focused through resolving slit 50 (apart from asmall percentage of ions that are deflected or neutralized throughcollision with the residual gas in the vacuum housing 20).

Referring to FIG. 6, a property of the magnetic analyzer system 21 isthat it disperses the beam wherein, at mass resolving aperture 50, ionsof mass m±Δm (102, 103) are separated by a distance Δx (101) from ionsof selected mass m (104) that travel along the center beam path 46.Unwanted ion masses can be stopped by either a blocking plate not shownor by the body 51 of the material used to form aperture 50. For the caseof conventional monatomic dopant ions a mass resolution of m/Δm≧60 isgenerally required—meaning that if ions of say mass 60 amu pass throughthe center of the resolving aperture 50, then ions of mass≧61 amu ormass≦59 amu are rejected. The principles of focusing and dispersiveeffects in dipole magnets are described in detail by Enge, Focusing ofCharged Particles, Chapter 4.2 Deflecting Magnets, Ed. A. Septier, pp203-264.

Referring to FIGS. 3 and 6, for the case when the beam center path 46 issubstantially orthogonal to exit pole edge 49, and the magnetic fieldbetween poles 26 over the region of the beam 22 about the center path 46is substantially uniform and vertical, the separation Δx for a massvariation of Δm/m is approximately

Δx=D(Δm/2m)  (2)

Where D is called the magnet dispersion and is given by

D˜R(1−cos φ)+b sin φ  (3)

In the above equation, R is the radius 53 of the center path 46, φ isthe angle 54 the ions bend through on passing through the magnet alongthe central path 46, and b (55) is the distance from the effective fieldboundary of the exit pole to the mass resolving aperture 50. In order toachieve a mass resolution of m/Δm with a resolving aperture width ofw_(r), it follows from Eqs. (1-3) that:

m/Δm=D/2w _(r) ˜D/|M|w _(s) ˜{R(1−cos φ)+b sin φ}/|M|w _(s)  (4)

As previously mentioned, a large source aperture width w_(s) is neededto extract high borohydride ion currents and meet present day waferthroughput requirements for dual polygate and source drain extensionboron implants. An important aspect of such magnetic analyzerembodiments is that they provide a multi-purpose system with a highenough mass resolution to also use conventional ions, even in the caseof a large source aperture width w_(s). It is found, referring to Eq. 3,this is achievable by using a sufficiently large radius R and bend angleφ. In one useful commercial embodiment, R=500 mm, φ=120°, b=195 mm, andM=−0.83, in which case, for a source aperture width of w_(s)=12.5 mm themass resolution is m/Δm˜88, and therefore sufficient for conventionalions. The significance of employing a large bend angle φ is shown inFIG. 7 where D/R is plotted against φ, for a conjugate image location ofb=195 mm. Doubling the bend angle from 60° to 120° more than doubles thedispersion D and hence mass resolution m/Δm.

Referring to FIGS. 8A and 8B, the space between the poles 26 where thebeam passes has a gap height G (106) which is typically between about 10to 20 nun greater than the height h_(s) of the source aperture in orderto provide clear passage of the beam through the magnet and also enablethe pole surfaces to be lined, e.g. with graphite (116) or silicon, toeliminate undesirable heavy metal impurities from being sputtered fromthe ferromagnetic pole material by beam strike. For a given maximummagnetic field capability, the mass of the magnet is proportional to theworking magnetic volume Vin the gap which, in turn, is the product ofthe path length through the pole, φR, the gap dimension G, and the polewidth W, i.e.

V˜φRGW  (4)

We have already observed from Eq. 3 that the requirement of a highdispersion in order to realize a mass resolution m/Δm≧60 for a widesource slit w_(s) requires large values of φ and R. Secondly, in orderto realize high borohydride ion current the gap G must also be large toaccommodate ions from the large height source aperture. Collectively,these requirements can only be realized, according to Eq. 4, with anappropriately high working magnetic volume and hence high magnet mass.Finally, in order to be able to carry out 4 keV boron implants, for dualpolygate implants, using 80 keV octadecaborane, the yoke and coil massmust be sufficiently high to support the correspondingly high magneticfield in the gap, which must be 12 kGauss, even for the case of abending radius of R=500 mm. According to Eq. 4, the only recourseavailable to minimize the working magnetic volume V is to minimize thepole width W (108). Unfortunately, the width cannot be arbitrarilyreduced in relation to the gap dimension G (106) and the cross-sectionaldimensions of beam 22 for otherwise second and higher order termsdevelop in the gap field, producing aberration from broadening the beamat the mass resolving aperture 50, which, in effect, would reduce themass resolving power. In one useful commercial embodiment, as shown inFIGS. 8A and 8B, the outer edges of the poles 26 are shaped withtrenches 112 and shims 111 that respectively lower and raise the surfaceof pole 26 towards the median plane 117. Two shims, one at each side,have width s₁ (107) and height h₂ (115) relative to the central region.Two trenches located immediately inwardly of the respective shims havewidth s₂ (109) and depth h₁ (114) relative to the tops of the shims.This technique is found to enable a significantly smaller pole width W(108) to be used in relation to the gap dimension G (106) and thecross-sectional dimensions of beam 22 yet maintain adequate control ofthe field shape in the working gap to prevent second, third and fourthorder aberrations from broadening the beam at resolving aperture 50.

To further control third order aberrations, another embodiment can useslightly different trench and shim parameters on the left and right handsides of the poles of FIG. 8A.

The example illustrated, having a nominally uniform gap G of 118 mm andpole width w of 166 mm, is sufficient to accept the beam emerging fromthe ion source aperture while providing space for liners 116 of graphiteor silicon that cover the pole face.

In the example, for achieving a simple robust design, the entrance andexit pole edges of the magnet are normal to the beam axes and there areno significant first order field gradients in the working gap of themagnet (i.e. the magnet does not produce any focusing in thenon-dispersive, vertical plane, this being handled by other provisionsdiscussed below). Consequently, in the dispersive plane, the conjugateimage points for the source object and mass resolving aperture 50 aresimply determined by Barber's rule (see Enge, Focusing of ChargedParticles, Chapter 4.2 Deflecting Magnets, Ed. A. Septier, pp 203-264).In a specific example, the object source point is set at 400 mm prior tothe effective entrance field boundary and the mass resolving aperture isat b=195 mm from the effective exit field boundary of the magnet. Theobject distance of 400 mm provides the space for pump 17 capable of highspeed vacuum pumping, for in-line vacuum isolation valve 23, and forwide energy range extraction optics system 14, 7.

While this design provides excellent performance over a wide range, forthe broadest aspects of invention, the magnetic analyzer system shouldnot be limited to the aforementioned description. One of ordinary skillin the art can appreciate a variety of implementations of the analyzeroptics to provide the desired multipurpose capability, including: theuse of magnetic fields between the poles that are non-uniform with firstand second order gradients to control focusing, aberrations, anddispersion; the choice of bending angle, radius, gap between the poles,and magnetic field range; the position of the ion source with respect tothe magnet entrance; the position and size of the mass resolvingaperture with respect to the magnet exit and the precise location withrespect to the conjugate image point; and the choice of particular poleshape shims and trenches to minimize second and higher order imagebroadening at the mass resolving aperture.

A frequently encountered characteristic of cluster ions, and one thatoccurs when borohydride ions containing many atoms of a doping speciesare used, is that ions are produced with different numbers of hydrogenatoms and therefore different masses. Referring to FIG. 9, a highresolution mass spectrum of ions generated by ionizing octadecaboraneB₁₈H₂₂ vapor in an ion source of the type employing a formed electronbeam such as described more fully below with respect to FIGS. 14 and15A, shows that a range of ion masses occurs, corresponding to theformation of singly charged ions containing different amounts ofhydrogen atoms and also different admixtures of the two isotopic boronmasses that make up the 18 boron atoms in an ion. From the point of viewof achieving a high ion current it is also clear from the spectrum inFIG. 9 that the total number of ions produced is spread over a widerange of mass peaks and therefore it is useful to accept all ions from amass of about 205 amu to about 220 amu, corresponding to m/Δm˜16. Inorder to transmit this entire range of masses through resolving aperture50, the width w_(r) of the mass resolving aperture needs to be betweenabout 4 to 6 times wider than for the case of implanting conventionalions in semiconductor wafers—e.g. an aperture range between about 8 and38 mm. A similar consideration applies to ions produced from decaboraneB₁₀H₁₄, where it is useful to accept ions with masses in the rangebetween about 113 amu to about 123 amu. Because the borohydride massesare much higher in value than masses of unwanted impurity ions, such awide resolving aperture, with a correspondingly lower mass resolution,is found acceptable. A mass resolving aperture width that iscontinuously or stepwise adjustable, from a small width for conventionalions to a large width to accept several peaks of borohydride ions, is animportant aspect of the embodiments of a multipurpose mass analyzersystem. The same considerations generally apply to other cluster ionsand specifically to the aforementioned examples of different usefulcluster ions.

Referring to FIGS. 10A, 10B, 10C, and 10D, one useful commercialembodiment of a continuously adjustable mass resolving aperture,comprises two geared, contra-rotating, eccentric water-cooled cylinders140 of stainless steel or other suitable non-ferrous materials.Cylindrical sleeves 142 of graphite fasten over the outside of thesecylinders in order to eliminate undesirable heavy metal impurities frombeing sputtered from cylinders 140 by the incident ion beam 144.(Sleeves 142 of silicon may similarly be employed). Cylinders 140 andtheir respective graphite sleeves 142 contra-rotate on eccentric centers143 and 145 creating an axially aligned, adjustable mass resolvingaperture width shown at a minimum width 150 in FIG. 10A, and at amaximum width 151 in FIG. 10B after a 180 degree rotation. In oneembodiment the minimum aperture width 150 is about 8 mm and the maximumis about 38 mm. Other values and ranges are possible by appropriateadjustment of the cylinder 140 and sleeve dimensions 142, and thelocation of rotation centers 143 and 145. Cooling water or othersuitable fluids can be passed through holes 146 in cylinders 140.Cooling is generally required to remove the heat generated by beaminterception, particularly in the case when ion beam 144 comprises highcurrent, high energy, conventional ions. An electric drive motor 148rotates cylinders 140 through gears 152 and a bearing block and rotatingvacuum seal 154. The entire assembly is mounted on flange 156 which canfit and seal into the analyzer magnet vacuum housing 20. A graphiteplate 159 with an exit aperture 161 can also serve as the firstelectrode of a decelerating system to be described below.

The adjustable mass resolving aperture (mass-selection slit) should notbe limited to the aforementioned description. One of ordinary skill inthe art can appreciate a variety of implementations, including:different geometrical arrangements for cooling, gearing, motor drive andmounting, rotation angles and vacuum sealing; the use of rotating vanesrather than cylinders; and the use of rectilinear rather than rotationalmotion.

An important aspect of the embodiment shown in FIG. 2 and FIG. 8A isthat the poles 26 penetrate through and seal into the vacuum housing 20,an arrangement, which, in effect, maximizes the magnetic efficiencybecause the space between the poles 26 is not reduced by the presence ofthe non-ferromagnetic material typically used for the construction ofthe vacuum housing. The magnetic efficiency is further improved becausethere is no air gap between the adjacent surfaces of the poles 26 andcores 28. The vacuum housing 20 and poles 26 are sandwiched between thesurfaces of the cores 28 but can be easily withdrawn withoutdisassembling the other parts of the magnet, which, in effect, minimizesthe cost of maintenance.

A sealing arrangement for the poles is shown in FIG. 8C. The pole isprovided with a laterally protruding rib 26A extending along each edgeof pole 26. Each rib is captured between a ledge 20A formed in thehousing wall at the opening for the pole and an overlying retainer strip27 that is secured to the housing by screw fasteners, not shown. Acompressible vacuum sealing element is captured and compressed in achannel formed between the outer edge surface of rib 26A and surfaces ofhousing 20 and retainer strip 27.

Referring to FIGS. 1 and 2 the pair of coil assemblies 40 of the dipolemagnet is contoured to closely encircle and follow the general plan viewshape of the poles 26 and cores 28 in order to minimize the straymagnetic flux outside the working gap between the poles and accordinglyminimize the weight and cost of the yoke pieces 30, 32, and 34. In oneuseful commercial embodiment shown in FIG. 4, coil assembly 40 caninclude four separate winding elements 80A, 80B, 80C, and 80D,electrically connected in series. Winding elements 80A-D can be, forexample, made of 60 turns each of copper strip 1.626 mm×38.1 mm indimension, and wound continuously with 0.08 mm thick inter-turnelectrical insulation. Insulation such as mylar or kapton are suitable.The coil current can be up to 240 A and the total voltage across thecoil terminals up to 120V dc, corresponding to a total coil power of28.8 kVA. This is sufficient to generate a magnetic field 24 in theworking gap between the poles 26 of greater than 10 kilo-Gauss for a gapdimension of 120 mm between the poles 26.

In one embodiment, three cooling plates 82B, 82C, and 82D are disposedbetween each pair of adjacently positioned winding elements 80A-D. Outercooling plates 82A and 82E are positioned on the outer surfaces ofwinding elements 80A and 80D. Cooling plates 82A-E can have any suitablethickness, for example, 10 mm. Cooling plates 82A-E provide a means forremoving or dissipating ohmic heat generated from the electric currentpassing through winding elements 80A-D. A cooling fluid such as watercan be circulated through cooling plates 82A-E via cooling tubes 84,e.g. copper tubes inserted in cooling plates 82A-E. An important aspectof the described structural embodiment is the electrical isolation ofcooling tubes 84 from winding elements 80A-D. In the case of watercooling, electrical isolation of cooling tubes 84 from winding elements80A-D significantly eliminates electrolysis and the need for usingde-ionized cooling water which, in effect, minimizes operating cost andmaintenance.

Referring to FIG. 5, in one embodiment, interleaved fiberglass cloth 81can be used as one means for electrically isolating winding elements80A-D from cooling plates 82A-E. The entire coil assembly 40 can also bewrapped with fiberglass tape and vacuum impregnated with epoxy resin, toeffectuate a single, rigid, impervious coil assembly 40. Coil assembly40 should possess high integrity against stress generated from thermalexpansion and contraction during operation. The resin impregnatedfiberglass between the edges of the winding elements 80A-D and theadjacent surfaces of cooling plates 82A-E provide high enough thermalconductivity for efficient transfer of heat which can be 29 kW in oneembodiment.

The embodiment of coil assembly 40 should not be limited to theaforementioned description. One of ordinary skill in the art canappreciate a variety of implementations, including: any workable numberof winding elements 80A-D and cooling plates 82A-E (for example two, andthree, respectively); other suitable materials used for winding elements80A-D such as aluminum. Additionally, winding elements 80A-E can be madeby using rectangular, square, or circular solid copper or aluminum wirerather than strip. In an alternative embodiment, rectangular, square, orcircular copper or aluminum tube can be used for the winding elements 80which can be directly cooled by passing a de-ionized cooling fluidthrough the hole of the conductor tube, rather than using indirectcooling by thermal conduction to cooling plates 82A-E.

Inter-turn insulation can be implemented by other methods and materials,such as wrapping the conductor with an insulating tape, sliding aninsulating sleeve over the conductor, or coating the conductor with aninsulating film, e.g. enameled copper or anodized aluminum.

In one embodiment the ion beam is capable of being decelerated afteremerging from mass resolving aperture 50. Deceleration can be helpfulfor the case of low energy, high dose implants because eitherconventional or borohydride ions can be extracted from the source andtransported through the analyzer magnet at a higher energy than thefinal implant energy. At such higher energy, the effects of internalspace charge forces and thermal ion temperature within the beam are lesslimiting on the magnitude of the beam current that can be realized atthe resolving aperture 50. In one embodiment, deceleration isimplemented by passing the beam through a sequence of threenon-ferromagnetic electrodes 60, 61, and 62, as shown in FIGS. 1 and 3.A decelerating voltage (V_(d)) 64, typically 0-30 kV in magnitude, canbe applied between electrodes 60 and 62 to decelerate ions to a lowerenergy. The decelerator embodiment shown in FIG. 1 can be incorporatedin the vacuum housing 20 and the final energy electrode 62 is isolatedfrom the housing 20 with insulator 66. In the presence of thedecelerating electric field space charge neutralizing electrons areswept out of the beam. The resulting diverging space charge forces arecounteracted by applying a voltage (V_(f)) 65 to intermediate focusingelectrode 61 via a feed-through 63 mounted on the vacuum housing 20. Thevoltage V_(f) is typically 0-30 kV negative with respect to electrode62.

The embodiments for the ion decelerator are not limited to the specificarrangement shown in FIGS. 1 and 3, and one of ordinary skill in the artcan appreciate a variety of implementations to optimize the iondeceleration for particular incident ion beam conditions, including: anynumber of workable electrodes (for example two, three, four—etc.);electrodes with circular or slot-shaped apertures; planar or curvedelectrodes, light or heavy non-ferromagnetic materials such as aluminum,graphite, or molybdenum for constructing the electrodes; and variousvacuum configurations wherein the electrodes are installed within themagnet vacuum housing 20 or in a separate vacuum housing depending onthe particular configuration of the ion implanter.

When the ion decelerator is activated, the magnet vacuum housing 20, andother parts of the magnet electrically connected to the vacuum housing,such as the poles 26, cores 28, and yoke parts 30, 32, and 34, all mustbecome electrically biased from ground potential by a voltagecorresponding to the decelerating voltage V_(d) (64), i.e. by a voltagein the range of 0-30 kV negative with respect to ground potential.

In one important aspect of the embodiment, the integral windings 80A-Dand cooling plates 82A-E are wrapped in porous insulating material suchas fiber glass and vacuum impregnated with epoxy to form an imperviouscocoon 86 around the entire coil assembly 40 approximately 6-8 mm inthickness. In another embodiment an insulating powder such as aluminumoxide can be used instead of fiberglass to fill the epoxy, and thecocoon formed using a casting mold. The insulating cocoon 86 enables thecoil assembly to be electrically isolated by up to a voltage of 30 kVfrom the remainder of the magnet structure, namely the cores 28, poles26, vacuum housing 20, and yoke pieces 30, 32, and 34. Therefore, thewindings 80A-D and the cooling plates 82A-E can remain nominally atground potential even though the remainder of the magnet may have up to30 kV negative bias with respect to ground potential—which, in effect,provides a substantial cost benefit because the coil power supplies 100(FIG. 2) can be operated at ground potential using standard grounded acpower 102. The embodiment described avoids the need to provide isolationof the coil power supplies 100 to 30 kV. More importantly, it alsoavoids the need to use a 30 kV isolation transformer for the 30-40 kVAinput ac power for the coil power supplies 100. A further advantage liesin the fact that the fluid cooling needed to remove the heat collectedin cooling plates 82A-E, for example 29 kW in one embodiment, can beprovided from a ground potential source 98 without the need to use ade-ionized fluid. In fact the cooling fluid can be regularnon-de-ionized tap water.

Referring to FIGS. 1 and 2, the current terminals 87 for the windingspenetrate the cocoon 86 at a location that is typically a distance of 40mm or greater from any neighboring components of the magnet to enable upto 30 kV electrical voltage isolation to be applied to the coil windings80A-D and cooling plates 82A-E without arcing and electrical breakdownoccurring between the coil terminals 87 and the magnet surround.Similarly, the cooling tubes 88 are brought out through the cocoon 86 ina manner that provides a safe working distance of at least 40 mm fromthe magnet surround, again to avoid arcing and electrical breakdown. Thecooling tubes are welded into manifolds 89 which are constructed withedge and corner radii in order to eliminate electrical coronas. They arealso positioned to avoid arcing and electrical breakdown to the magnetsurround.

The current leads 90 and cooling lines 92 pass from the coil to a groundsurround 96 via insulating PVC sleeves 94 passing through the magnetyoke return 32.

The embodiments for forming the isolating cocoon and bringing windingterminals and cooling tubes outside the coil should not be limited tothe aforementioned method. One of ordinary skill in the art canappreciate a variety of implementations including using different typesof epoxy recipes and insulating materials.

Referring to FIG. 1, following magnetic analysis, the beam passesthrough a magnetic quadrupole triplet 210 and finally transportedthrough a beam-line 76 under vacuum to the wafer process chamber 72 toirradiate wafer 70. The wafers are processed serially one at a time, orseveral at a time by repeated mechanical passage of a batch wafersthrough the beam. Wafer 70 is admitted from and withdrawn to a cleanroom area via appropriate electromechanical mechanisms, doors and vacuumlocks.

The embodiments of the beam-line and process chamber are not limited toa particular configuration. For example, as one of ordinary skill willappreciate, the beam-line may be simply a ballistic drift region, or itmay have a number of other features including; ion optic elements suchas a bending magnet to filter out neutral particles generated in thecase when the beam is decelerated prior to entering quadrupole triplet210—such neutral particles have a higher energy than the deceleratedions and if they are not filtered out of the beam they are more deeplyimplanted in wafer 70 which can significantly degrade semiconductordevice performance. Beam line 76 may also contain magnetic or electricbeam scanners, with associated collimator magnets, to parallel scan thebeam in one direction across the wafer. This can be advantageous in acommercial implanter because then the wafer only needs to bemechanically scanned in the orthogonal direction to the beam scandirection to finally achieve a uniform dose.

Referring to FIG. 12A, the magnetic quadrupole triplet 210 is useful incommercial ion implanters, for the cases of both conventional andcluster ions, irrespective of the details of the components in thedownstream beam-line 76. Firstly, the strength of the magnetic fields ofthe three individual elements 211, 212, and 213, of the quadrupoletriplet can be independently adjusted to control the dimensions andangular divergence in both the vertical and horizontal directions of thebeam at the wafer 70 and thereby optimize the beam implant conditions onwafer 70. This is important in a commercial ion implanter in order toachieve high quality implants, especially as the downstream componentsin the beam-line usually do not have readily adjustable, broad range,focusing capability. Secondly, in the cases where prior deceleration ofthe ion beam occurs, the quadrupole triplet is also useful to controlthe beam divergence that often occurs, at least in one direction,following the deceleration process. In one common embodiment the beamentering quadrupole triplet 210 is ribbon shaped with the long directionin the vertical direction. In this case the first element 211 isoperated with a polarity that causes focusing in the vertical direction,with corresponding defocusing in the horizontal direction. The secondelement 212 has polarity opposite to 211 causing horizontal focusing andvertical defocusing. Finally, the third element 213 has the samepolarity as the first element 211. The focus (F) and defocus (D)combinations are therefore DFD in the horizontal plane and FDF in thevertical plane. By using appropriate field strengths in each of theelements 211, 212, and 213, respectively, overall net focusing issimultaneously achieved in both vertical and horizontal planes.

Very importantly, in the case of the cluster ions, when mass resolvingaperture 50 is set wide enough to transmit a range of ion masses, forexample, from between about 205 amu to 218 amu for the case ofoctadecaborane, or from between about 108 amu and 115 amu for the caseof decaborane, the individual magnetic field strengths of the quadrupoleelements of the triplet can be adjusted to simultaneously andsubstantially remove angular deviation at wafer 70 that can otherwisegenerally occur in the case where there is a range of different massesin the ion beam. Referring to FIG. 12A selected, ions of mass m±Δm enterthe quadrupole along horizontal paths that are displaced and at slightlydifferent angles from the central ion path corresponding to an ion massm. As described previously, in connection with FIG. 1, these separationsare generated as the multiple mass ions are transported through theanalyzer magnet. By appropriate adjustment of the DFD focusing sequence,the ion paths 203 emerge from the quadrupole approximately parallel toeach other. Eliminating such angular deviation is important commerciallybecause it enables high currents of cluster ions to be used in lowenergy, high dose implant applications, without deteriorating theimplant angle quality on wafer 70 as a result of there being more thanone ion mass in the beam impinging on the wafer.

When one or more mass dispersive elements are in the beam line beyondthe quadrupole triplet, the differential adjustments of the triplet cancompensate for the mass dispersive effects of these downstream elementsas well as that of the analyzer magnet for the entire range of differentmass cluster ions.

Referring to FIGS. 12A and 1233, in one embodiment the quadrupolemagnetic fields are generated by passing electric current through coils206. Each quadrupole element has four coils wound separately around fourferromagnetic core pieces 217. The core pieces fasten to ferromagneticpole pieces 214 which penetrate and seal through vacuum housing 219constructed from non-ferromagnetic material such as aluminum orstainless steel. Adjacent coils are wound with opposite polarity inorder to create a so-called quadrupole field in the region between thefour poles. Magnetic flux is returned from one pole to another via corepieces 217 which are magnetically coupled via ferromagnetic yokestructures 221. The windings of coil 206 are made from rectangularsection copper tube 215 which are directly cooled with water or othersuitable cooling fluids. Graphite liners 216 prevent beam strike fromsputtering heavy ion contaminants off surfaces of poles 214, and theinternal walls of vacuum housing 219.

The quadrupole structure should not be limited to the aforementioneddescription of FIGS. 12A and 12B, and one of ordinary skill in the artcan appreciate a variety of implementations, including: using two ratherthan three elements to provide DF and FD sequences to obtain overallfocusing in the vertical and horizontal planes; and the use ofelectrostatic rather than magnetic quadrupole fields.

One embodiment, suitable for ion implanting with cluster ions as well asconventional ions, and employing a magnetic scanning beam-line is shownin FIG. 13. A ribbon shaped beam 300 is extracted from an ion sourcewith an aperture width w_(s) of 12.5 mm and a height h_(s) of 100 mm,such as described in association with FIG. 1. The beam is magneticallyanalyzed with a 120 degree sector bending magnet 302 having isolatedcoils 304 as previously described and shown in FIGS. 2, 4 and 5. Thepole shape has pole edge shimming as shown in FIGS. 8A and 8B and aspreviously described. The beam passes through an adjustable massresolving (selecting) aperture as shown in FIGS. 10A-D, a threeelectrode decelerator unit 306 as shown in FIG. 3 and a magneticquadrupole triplet 380 as shown in FIGS. 12A and 12B. The beam thenpasses through a magnetic scanner 310 and collimator 312 whichcollectively parallel scans the beam in a horizontal direction from oneside 320 to the other side 321 across wafer 70. Referring to FIG. 13, aschematic illustration is shown of the beam 314 on one side of thewafer, 318 at the center of the wafer, and 316 on the other side. Animportant aspect of the embodiment is the fact that the beam scanner andthe collimator both bend the beam in the same sense. Consequently, theion beam path lengths and magnetic focusing properties of combinedscanner and collimator are similar for the three beam positions 314,318, 316. Consequently, irrespective of the horizontal scan position ofthe beam on the wafer, one set of field strength settings can be foundfor the three magnetic quadrupole elements which simultaneously optimizethe beam size, angular spread, and, very importantly, eliminate angulardeviations in the case when multiple mass borohydride ions and clusterions in general are used.

In one useful commercial embodiment of the beam-line shown in FIG. 13,the previously described beam line parameters have the following values:

-   -   A. Analyzer Magnet: R=500 mm, φ=120°; G=118 mm; s₁=31 mm; s₂=8.6        mm; h₁=8.7 mm; h₂=4.7 mm; W=166 mm; bending power=80 keV        octadecaborane, accepting ions from source aperture w_(s)=12.5        mm and h_(s)=100 mm.    -   B. Mass selection aperture: about 8 mm minimum to about 38 mm        maximum, continuously adjustable.    -   C. Decelerator Electrodes; three planar with aperture sizes 50        mm wide×118 mm high.    -   D. Quadrupole triplet: aperture: 80 diagonal between pole tips;        pole tip field adjustable 0-5 kGauss.    -   E. Beam Scanning Magnet; Vertical gap=80 mm; Bending power-80        keV octadecaborane.    -   F. Collimator: Bending radius 900 mm; Pole gap=80 mm; bending        power=80 keV octadecaborane.        The total deflection produced collectively by scanner 310 and        collimator 312 is 30 degrees. The bend direction is opposite to        the bend direction of the analyzer magnet in order to minimize        the width of the ion implanter, which is an important        consideration that in effect reduces cost and installation        footprint.

The beam size and angular divergence at the wafer are controlled bydifferentially adjusting the strength of the individual quadrupoleelements in the quadrupole triplet. Importantly, in the case of theborohyride ions and cluster ions in general, the triplet alsocompensates for the collective mass dispersion introduced by theanalyzer magnet, magnetic beam scanner, and magnetic collimator. Byappropriately setting the quadrupole element strengths, the angulardeviation arising from the multiple mass components can be substantiallyremoved, i.e. reduced to less than 0.15 deg over the entire scan range.

High energy particles remaining in the beam after deceleration followingthe mass selection aperture do not reach the wafer because they arefiltered out of the beam by the combined beam deflections of the scannerand collimator.

The ion source 11 of FIGS. 14 and 14A for use in the embodiments ofFIGS. 1 and 13 produces cluster ions, for example the borohydride ionsB₁₈H_(x) ⁺ or B₁₀H_(x) ⁺ from B₁₈H₂₂ or B₁₀H₁₄ a vapor. As explainedpreviously in reference to FIGS. 1 and 6, and as shown in greater detailin FIGS. 14 and 15B for this embodiment, the ions are extracted from anionization chamber by an electrostatic extraction electrode systemcomprising a suppression electrode and ground electrode, the ions beingdrawn through an extraction aperture 12 in the form of avertically-oriented slot in the front plate of the ion source bodyhaving width w_(s) and height h_(s). The dispersive plane for the ionbeam line is in the direction of width w_(s) in FIG. 15A, while thenon-dispersive plane is in the direction of height h_(s) in FIG. 15B.

FIG. 14 shows dispersive plane cross sections of two variations of thecluster ion beam extraction system. The extraction system consists ofthree plates: The ion extraction aperture (I), through which the ionsare extracted from the ion source at source potential (e.g., 60 kV aboveterminal potential), suppression electrode (II) typically held a few kVbelow terminal ground potential to suppress any backstreaming electrons,and ground electrode (III), held at terminal potential.

Extraction aperture plate (I) is about 20 mm thick. The flat sectionadjacent to the extraction aperture is identical for both variations(1). In the first case, the bevel has a uniform angle throughout thethickness of the plate, whereas in the second case, there is a doublebevel of increasing angle.

The system of either design is adjustable over a wide angle.

The embodiment of FIGS. 14, 14A, 15A and 15B utilizes a formed beam 330of accelerated electrons to produce cluster ions within ionizationchamber 10′. This type of ion source produces a sufficient density ofmolecular ions to enable the extraction electrode 14′ to extract acurrent density of up to about 1 mA/cm² from the slot aperture 12′machined in front plate 370 of the ion source body. In a preferredembodiment for use in FIGS. 1 and 6 the slot dimension is about 100 mmhigh, h_(s), by 12.5 mm wide, w_(s). Slots of greater or lesserdimensions will yield a correspondingly greater or lesser amount oftotal extracted ion current, with substantially similar peak extractedcurrent density.

Using principles previously described by T. Horsky, the ion source 11′of these figures uses impact of energetic electrons of beam 330, FIG.14, to provide the gentle ionization necessary to preserve the integrityof the vapor molecules being ionized. Such an ion source, whenconstructed to provide good beam current performance using vapors ofborohydride feed material, also is capable of producing several mA ofarsenic and phosphorus ion beams from arsine and phosphine gas, using atraditional gas box and gas feed to the ionization chamber 10′. The ionsource of FIG. 14 employs a remotely positioned electron gun 340 thatcomprises a filament and electron optical system external to theionization chamber 10′ to produce the formed beam 330 of acceleratedelectrons. Filament wear associated with ion erosion is thus minimized,helping to ensure long filament life. The externally generated,energetic electron beam 330 creates a region of ions just behind thelong rectangular slot 12′ along its entire length from which ions areextracted by the ion optical system. For this purpose, the electron gun340 creates an electron beam of between 1 mA and 100 mA. The beam isdeflected through 90 degrees by a Magnetic dipole field. Once deflected,the beam is injected into ionization chamber 10′ to traverse a verticalpath parallel to the length of the extraction slot aperture 12′. Theelectron beam is confined to this path by vertically-oriented magneticfield 350, the magnetic confinement being optimized for each design tomaximize the ionization efficiency of the injected electron beam. Afterpassing behind the extraction aperture 12′, the unused portion ofelectron beam 330 is intercepted by beam dump 360.

By varying the electron emission current and also the flow of feedmaterial into the ion source 11, a stable electrical ion beam current ofbetween 5 μA and 3 mA can be achieved. As an example, B₁₈H₂₂ or B₁₀H₁₄vapor is typically introduced into the ion source from an externallymounted heated vaporizer, through a pressure control device whichregulates the flow of vapor into the ionization chamber 10′. For feedmaterial in the form of source gases such as arsine and phosphine aseparate gas feed passage is provided to the ionization chamber.

Advantages of such a large gap beamline system, even when employed withconventional ions, include larger total beam current and bettertransport of the beam. By use of the large extraction aperture, andextraction at lower ion density, Child-Langmuir limits on ion beamcurrent density are avoided and larger total beam current can beextracted for transport through the large gap system. Also, because ofthe lower ion density, and hence lower charge density in the extractedion beam (relative to that of a conventional Bernas-type source), thebeam blow-up caused by internal Coulomb space charge forces is reduced.This enables the ion beam to reach the target with less angulardivergence, and improved uniformity of angle of incidence upon thetarget surface. Space charge forces as well as thermal motion stillcause the extracted ion beam to tend to expand in both the dispersiveand non-dispersive directions. The ion optical extraction system ofFIGS. 15A and 15B is constructed to effectively form and focus the ionbeam in the dispersive and non-dispersive planes by application of lensvoltages.

FIG. 15A shows the front plate 370 of ion source chamber 10′, extractionslot aperture 12′ formed in the plate, suppression electrode 14′, andground electrode 7′, all in horizontal cross-section, with thedispersive plane in the plane of the figure. In the dispersive plane,the ion beam 19′ is focused at w_(b) into the acceptance of the analyzermagnet 21 of FIG. 1. The position of the electrode elements 7′ and 14′with respect to the aperture plate 370 of the ion source along the beamdirection is variable by motion control devices which are known in theart.

In this preferred embodiment, as shown in FIGS. 15 and 15B, the frontplate 370 of the ion source chamber 10′ is formed as a knife edge 12A atthe slot aperture 12′ to also serve as an adjustable lens element. Forthis purpose the aperture plate 370′ is electrically isolated byinsulator 12B from the remainder of the ion source body as previouslydescribed by T. Horsky, et al.

The focal length of this lens system in the dispersive plane forproducing the beam waist w_(b) is dictated by the beam energy and theposition of the electrode elements, as well as by their shape andapplied voltages. As previously described, the beam 22 is then focusedby the analyzer magnet to form a conjugate image in the dispersive planeof width w_(r) at the mass selection aperture 50, as described inrelation to FIG. 3, following which the beam 210 reaches the quadrupoletriplet with appropriate size to enter the triplet. The typical beamenvelope in the horizontal plane passing through the triplet 210 isrepresented in FIG. 16A for the case of the central mass peak. Theseparation and principal ray paths for the range of mass peaks haspreviously been described in FIG. 12A.

In the systems of FIGS. 1 and 13, focusing in the “Y” (non dispersive)plane to the quadrupole triplet 210 is accomplished by the extractionoptics of the ion source as no “Y” direction focusing occurs in theanalyzer magnet. In the embodiment of FIG. 15B, to focus the ion beam inthe non-dispersive plane, the suppression and ground plates 7′ and 14′,as well as the knife edge 12A of the extraction slot 12′, are fabricatedwith a radius of curvature, such that each presents a convex profile tothe ion source, and a concave profile to the downstream beam line. Thiscurvature, as shown in FIG. 1B, produces convergence of the height ofthe extracted beam 19′. In the embodiment, a radius of curvature R of 1meter is employed. In other embodiments other radii are possible; ingeneral, smaller radii applied to the extraction plates produce ashorter non-dispersive plane focal length, and hence a greater degree ofconvergence, and vice versa with respect to larger radii. By use of thetriode thus formed, simple and space-efficient focusing in thenon-dispersive plane is thus accomplished and, referring to FIG. 16B,the analyzed beam 22′ reaches the quadrupole triplet 210 within anenvelope sized in the non-dispersive plane to enter the triplet 210.

The degree of beam convergence produced by the extraction optics of theion source in the non-dispersive plane of the analyzer magnet varieswith the magnitude of the total cluster ion beam current and the ionenergy and is optimized to size the beam to be accepted at the entranceto the quadrupole over a wide range of beam currents from a fewmicroamps to a few milliamps, and a wide range of energies, from about 4keV to 80 keV. The quadrupole triplet provides final optimization of thebeam size and angular divergence at the wafer in both the non-dispersive(vertical) and dispersive (horizontal) planes at the wafer 70.

The embodiment of a system for non-dispersive plane focusing of the beamprior to the analyzer magnet, however, are not limited to a particularconfiguration. Systems are possible in which the aperture plate does notserve as a lens element, or additional lens elements may be employed, ora quadrupole focusing element may be included.

By providing non-dispersive plane focusing by an optical systempreceding the analyzer magnet, the demands upon the analyzer magnetdesign are simplified while providing highly efficient ion beamtransmission through the analyzer magnet and the post-analysisquadrupole triplet 210. Along with the reduced divergence obtained withlow density ion extraction, this tends to reduce strike of ions on thepassage walls, leading to fewer detrimental deposits, greater usefulbeam current and less contamination of the beam. As shown in FIG. 16B, athus-produced, well-collimated beam with a vertical height of about 6 cmcan be injected into the quadrupole triplet with the non-dispersiveplane focusing shown, even though the beam was generated from anextraction slot of 10 cm. height.

FIG. 17 shows magnetically scanned boron particle currents, derived fromoctadecaborane, employing the scanning system according to FIG. 13 andthe ion source according to FIGS. 14, 15A and 15B. The current wasmeasured at the exit port of the vacuum housing of collimator 312 inFIG. 13. The beam current was essentially unchanged over the entire scansweep frequency range from dc to 170 Hz. These measured particle beamcurrents are very much higher than hitherto reported from conventionalfixed beam, high current ion implanters. Furthermore, these beamcurrents were achieved without the need to use deceleration just priorto the wafer, a technique often used in conventional high currentimplanters to enhance the low energy beam current but having thedisadvantages of (a) introducing large angular spreads of severaldegrees in the ions impinging on the wafer, and (b), allowing highenergy particles neutralized prior to or during deceleration to reachthe wafer, in the absence of neutral particle filtering afterdeceleration. Such high energy particles penetrate further into thewafer and generally degrade the implant quality, which is undesirablefor the production of present-day very shallow CMOS junctions.

It is well known that it is very difficult to extract and magneticallyanalyze from a Bernas type ion source, very high beam currents (morethan 5 mA) at low energy (less than 10 keV) of monatomic doping ionssuch as B⁺, P⁺, and As⁺. Even if high currents can successfully beextracted from the source itself, the injection into and transportaround the magnetic analyzer proves to be difficult because at lowenergies the ionization cross-section for the ions to form space chargeneutralizing electrons within the ion beam is very small and falls veryrapidly with decreasing energy below the energy regime of 10-15 keV.Attempts to improve the beam neutralization by directly insertingelectrons into the beam, or introducing them via a plasma gun aregenerally thwarted by the very presence of the magnetic field of theanalyzer itself and are therefore techniques generally not of benefit tocommercial ion implanters.

Yet another well known technique is to bleed a gas or vapor into theregion inside the vacuum housings of the ion source and/or analyzermagnet and thus flood the beam path with a higher pressure of gas in thehope of generating more space charge neutralizing low velocity negativeions within the beam. P⁺, and As⁺ ion currents have been moderatelyincreased with a gas bleed of nitrogen, but this generally reduces theB⁺ ion current. Sinclair et al. (U.S. Pat. No. 5,814,819 Sep. 29, 1998)has found that water vapor can enhance the monatomic boron current thatcan be extracted from a Bernas type ion source and transported throughthe analyzer magnet. These methods of neutralization have not beenwidely successful or adopted in commercial implanters because the highbeam currents at low energy generally exceed the physical conditions ofplasma stability particularly in the presence of the analyzer magneticfield. Consequently, the generated ion beams are often unstable, theinstabilities being trigged by small statistical fluctuations in thebeam size and current being extracted from the ion source. The beamcurrents are often not reproducible and can depend too critically on theprecise ion source parameter tuning and changes associated withtemperature variations.

An advantage of the cluster type ion source represented in FIGS. 14,14A, 15A, and 15B is that additional background gas neutralization isnot generally required because the actual cluster ion beams are at amuch higher energy and a much lower current than for the case ofcomparably useful monatomic ion beams, and as a consequence theconditions that lead to plasma instability are avoided.

In the case of a long beam line as represented in FIG. 13, where thepath length from the exit of the analyzer to the wafer is greater than 2m and even as long as 3 m in order to accommodate the beam linequadrupole, scanning magnet, collimator magnet, and a 0.5-0.7 m driftthrough the final process chamber, it has been found useful at lowenergies wherein the ion beam is not fully neutralized with electronsand wherein the beam has to pass through magnetic fields such as thescanner and collimator, to add a small amount of electronegative gassuch as SF₆ in the scanner and collimator regions to improve the beamtransmission to the wafer and reduce the beam size at the wafer, both ofwhich result in improved wafer throughput and implantation efficiency.

Referring to FIGS. 13 and 17, at single particle implant energies belowabout 1 keV the beam current on the wafer can be significantly enhancedby a factor of 1.5-2 by admitting a small amount of SF₆ gas 305 into thevacuum housing of the sweep Magnet 310 via a flow control valve 307 anda tube 309. This is because SF₆ readily forms negative ions within thecluster ion beam via interaction with the cluster ions. Such negativeheavy ions have a low mobility and being energetically trapped withinthe electric potential well of the beam are effective in neutralizingthe internal space charge forces within the beam that otherwise wouldcause the beam to blow-up beyond the acceptance aperture of the beamline. The presence of SF₆ also significantly reduces, by 50-70%, thetransmitted beam size at the wafer as a result of reducing the beamblow-up in the drift region between the exit of the collimator 312 andthe location of the wafer 70. Typical flow rates of SF₆ needed toenhance the beam current are 0.1 standard cc per minute producing apressure rise of only 2-3E-6 torr. SF₆ is a relatively inert gas and itsuse at such a low pressure is thought not to be generally detrimental toimplant processes either directly or via interaction with the clusterion beam itself.

Referring to FIG. 17A, below 1 keV and especially below 0.5 keV, thebeam current is further enhanced in the embodiment shown in FIG. 13, byactivating the three electrode decel system 306 shown in FIG. 3. Atoptimum operation the decel ratio is approximately 2:1 meaning that thefinal decelerated energy is about half the energy of the beam passingthrough the analyzer magnet 302. The voltage V_(f) 65 on the centerfocusing electrode 61 (see FIG. 3) is slightly more negative by about1-3 kV than the analyzer vacuum housing 20 of the analyzer magnet.Although the phenomena is not completely understood, it has been foundin the low energy regime that the beam current is improved by 10-30% byapplying just a small decel voltage V_(d) of about 100V.

As shown by the data in FIG. 17A, the use of a neutralizing gas such asSF₆, injected in the region following the decel system 306, isparticularly effective, because of the low energy of the beam followingdeceleration, and the susceptibility to space-charge blow-up in a longbeam line, such as that shown in FIG. 13.

One of ordinary skill in the art can appreciate other implementations ofusing gas or vapors to substantially neutralize the intrinsic positivespace charge of low energy ion beams, including: using otherelectronegative gases such as water vapor (H₂O) or BF3 and admitting thegas or vapor into other regions after the analyzer magnet of a long beamline, such as in the quadrupole or collimator vacuum chambers, whereinthe beam is susceptible to space-charge blow-up at low energies.

The performance of this system shows the practicality of and thetremendous improvement in drift-mode beam current that can be realizedby using cluster ions in general and borohydride ions in particular. Theresults pave the way for a new generation of ion implanter tools andhave put to rest previous and somewhat widely held concerns that suchbeams could turn out to be difficult to transport, and even moredifficult to scan, in the vacuum system and general beam linearchitecture commonly used in ion implanters. Even with the long beampath through the scanning and collimator magnets, gas attenuationmeasurements show that the beam loss from gas scattering,neutralization, and ion break-up, is only a few percent.

Alternative embodiments of FIGS. 1 and 13 employ a dual mode ion source.As previously described by T. Horsky, one form of a dual mode ion sourcecan operate in either the electron impact mode that has just beendescribed, e.g. to produce the molecular ions, or in an arc dischargemode, to produce high currents of monomers and multiply-charged ions.The ions produced in each mode of operation can be extracted through thesame slot-form aperture by the same ion optical system, and pass throughthe same large gap of the analyzer magnet and through the ion implanterbeamline described herein, with of course suitable variation of themass-selection aperture 50 of FIG. 4 or FIGS. 10A-10D. Thus, advantagecan be taken of the mass resolution≧60 for monomer dopants, using anarrow aperture, e.g. of 6 to 8 mm, while a much larger mass selectionaperture is employed for molecular ions having multiple dopant atoms,for instance an aperture of 28 or 29 mm for ions of B₁₈H_(x) andB₁₀H_(x), to utilize the current from a number of mass peaks.

In one preferred form, a dual mode ion source is constructed to have anelectron gun to provide a formed electron beam and a separate arcemitter. For electron impact ionization, only the electron gun is used;to produce large monomer currents and multiply-charged ions, only arcoperation is used, the arc emitter striking a plasma discharge similarto that of a Bernas-type source, through typically of intensity lowerthan commonly used in Bernas sources. Such a dual mode ion sourceincorporates both vapor and gas inlet passages.

An example of a dual mode ion source is shown in FIG. 18. Ion source 11″is similar to that of FIG. 14 but the beam dump 360 of FIG. 14 isreplaced by member 280 that, during arc discharge mode, serves as anindirectly-heated cathode, heated by filament 390. As is known ingeneral, the use of an indirectly-heated cathode permits longer lifetimethan a bare filament emitter due to its filament being remotely locatedin a high vacuum environment, away from the source plasma.

In electron impact ionization mode, electron gun 340′ and the associatedmagnetic fields of the embodiment of FIG. 18 perform in the same manneras described for FIG. 14. The unused portion of the electron beam may beintercepted by a beam dump provided by member 380 (the member that isswitched to serve as cathode during the arc discharge mode).

In arc discharge mode, the electron gun 340′ is not used. The cathodemember 380 is energized by heating filament 390 to produce an arcdischarge to the walls of the chamber 10″. This creates a plasma columnalong the direction of magnetic field 350′, the magnetic field typicallybeing less than about 100 Gauss, however being sufficiently large toprovide plasma confinement. In an embodiment which takes advantage ofthe large-gap beam transport optics of the foregoing figures describedherein, the ion extraction slot 12″ may be 80 mm in height, h_(s), and10 mm wide, w_(s). In other embodiments that can also be employed withthe large-gap beam transport described herein, the extraction slot canfor instance be increased to 100 mm in height to 12.5 mm wide, whilestill achieving a mass resolution of greater than 60. Other smallerdimensions are also possible. Due to the large extraction area of theseembodiments relative to conventional Bernas-type plasma sources, as wellas due to the less intensity of the arc discharge, the plasma densityproduced in arc-discharge mode is less than with a typical Bernassource, but typically greater than 10¹¹ ions/cm³ and very useful for auniversal ion implanter capable of providing medium dose conventionalimplants as well as high dose, low energy cluster doping and materialmodification implants.

Referring to FIG. 19, another embodiment is shown for a medium currention implanter. For operation with borohydride ions, ions of differentmasses 416, 417, 418 are extracted from ion source 410 through aperture412 by applying a voltage to extraction electrode 414. The ions thenpass into a 90 degree analyzing magnet 426, and then through anadjustable resolving mass selection aperture 450. A cylindrical threeelectrode post accelerator structure 441, 442, 443 can post accelerateor decelerate the ions from the source extraction energy of 40 keV togive a final energy in the range 5-250 keV. The center electrode of thepost accelerator can be supplied with an adjustable voltage to obtainvarious degrees of focusing of the ion beam as it passes through thepost accelerator region and quadruples 440 and 441, magnetic orelectric, located on either side of the post accelerator. Following thepost accelerator there is a final energy magnet 444 which removes ionsor neutral particles that have been generated with an incorrect energyduring post acceleration (or deceleration). The final energy magnet isfollowed by a magnetic scanner 446 working in conjunction withcollimator 448, which bends the beam in the same sense as the scannermagnet 446.

The strength of quadrupoles 440 and 441 in conjunction with thepost-accelerator focusing electrode 442 voltage can be adjusted tooptimize the beam size and angular divergence in the vertical andhorizontal directions at wafer 70. Furthermore, very importantly, forborohydride ions, and indeed cluster ions in general, it is alsosimultaneously possible to minimize the angular deviation that wouldotherwise result in the presence of multiple mass ions. Because of thepresence of the final energy magnet 444, it is also possible to adjustthe strength of quadrupoles 440 and 441 in conjunction with thepost-accelerator focusing electrode 442 so that not only is the angulardeviation from multiple mass ions substantially eliminated, but also thehorizontal broadening from the presence of multiple mass ions can besubstantially eliminated in the beam as it scans across wafer 70. Thepaths of the central rays for the different mass ions 416, 417, 418cross over at 419 near the focus electrode 442. This compensates for thesubsequent, collective mass dispersion occurring in the final energymagnet 444, the beam scanner magnet 446, and the collimator 448. Such afeature is commercially useful in a medium current implanter to improveimplant quality and maximize wafer throughput.

The ion source and extraction optics employed in the embodiment of FIG.19 may be suitably scaled versions of those described with respect toFIGS. 14-16B and FIG. 18.

A number of embodiments have been described. Nevertheless, it will beunderstood that various modifications may be made without departing fromthe spirit and scope of invention. Accordingly, other embodiments arewithin the scope of the following claims.

1. A multipurpose ion implanter beam line configuration comprising amass analyzer magnet followed by a magnetic scanner and magneticcollimator combination that introduce bends to the beam path, the beamline constructed for enabling implantation of common monatomic dopantion species cluster ions, the beam line configuration having a massanalyzer magnet defining a mass selection aperture and a pole gap ofsubstantial width between ferromagnetic poles of the magnet, theanalyzer magnet sized to accept an ion beam from a slot-form ion sourceextraction aperture of at least about 80 mm height and at least about 7mm width, and to produce dispersion at the mass selection aperture in aplane corresponding to the width of the beam, the mass selectionaperture capable of being set to a mass-selection width sized to selecta beam of the cluster ions of the same dopant species but incrementallydiffering molecular weights, the mass-selection aperture also capable ofbeing set to a substantially narrower mass-selection width and theanalyzer magnet having a resolution at the mass selection aperturesufficient to enable selection of a beam of monatomic dopant ions ofsubstantially a single atomic or molecular weight, the magnetic scannerand magnetic collimator being constructed to successively bend the ionbeam in the same sense, which is in the opposite sense to that of thebend introduced by the analyzer magnet of the beam line.
 2. The ionimplanter beam line of claim 1 in which the mass selection aperture iscapable of being set to a first setting for monatomic ion species and asecond setting of at least fifteen times the mass-selection width of thefirst setting for accepting cluster ions generated from boron-containingcompounds.
 3. The ion implanter beam line of claim 1 or 2 in which theresolution of the mass analyzer magnet at the mass selection aperturefor monatomic doping ions is at least
 60. 4. The ion implanter beam lineof any of the foregoing claims in which the mass analyzer magnet issized constructed and arranged to form at the mass selection aperture aconjugate image in the mass dispersive plane of the width of the ionsource extraction aperture.
 5. The ion implanter beam line of claim 4 inwhich the mass selection aperture of the analyzer magnet is capable ofbeing set to an aperture width of at least 30 mm.
 6. The ion implanterbeam line of any of the foregoing claims in which the analyzer magnet isconstructed to analyze a beam extracted from a slot-form ion sourceextraction aperture of at least 12 mm width and 90 mm height.
 7. The ionimplanter beam line of claim 6 in which the mass selection aperture iscapable of being set to a first setting for the monatomic ion speciesand to a second setting of at least fifteen times the mass-selectionwidth of the first setting for accepting cluster ions of multiple massesnear a peak of interest, and the resolution of the mass analyzer magnetat the mass selection aperture for monatomic doping ions is at least 60.8. The ion implanter beam line of any of the foregoing claims in whichthe slot-form extraction aperture width is about 12.5 mm and heightabout 100 mm.
 9. The ion implanter beam line of any of the foregoingclaims in combination with an ion source constructed to produce ions ofcurrent density up to about 1 mA/cm² by an ionization mode employing aformed electron beam, the ion source constructed to receive feedmaterial alternatively in the forms of gas and heated vapor.
 10. The ionimplanter beam line of any of the foregoing claims in which the ionsource is constructed to function alternatively in a second ionizationmode employing arc discharge.
 11. The ion implanter beam line of any ofthe foregoing claims including means to introduce, downstream of theanalyzer magnet, a gas to generate negative ions within the ion beam byinteraction of the gas with the ion beam.
 12. The ion implanter beamline of any of the foregoing claims in which the analyzer magnet is asector magnet constructed to produce an adjustable magnetic field in thepole gap including a field exceeding about 10 kGauss.
 13. The ionimplanter beam line of any of the foregoing claims constructed to selectabout 80 keV ions generated from ocatadecaborane.
 14. The ion implanterbeam line of claim 1 in which the mass analyzer comprises a sectormagnet having a radius R of about 500 mm, a sector angle Φ of about 120degrees, a distance b from the effective pole exit boundary to the massresolving aperture of about 195 mm, the mass analyzer having amagnification M of about −0.83, the analyzer magnet constructed toanalyze an ion beam from a source having an extraction aperture width ofabout 12.5 mm, the analyzer magnet having mass resolution m/Δm of theorder of about
 88. 15. The ion implanter beam line of claim 1 includinga multiple element quadrupole focusing lens in the portion of the beamline following the analyzer magnet, the lens arranged to control thedimensions of the beam in orthogonal directions of the beamcross-section.
 16. The ion implanter beam line of claim 15 in which thelens has at least three quadrupole elements and is constructed tosimultaneously control the dimensions and angular divergence of the beamin orthogonal directions of the beam cross-section.
 17. The ionimplanter beam line of claim 16 in which the lens is a quadrupoletriplet focusing lens.
 18. The ion implanter beam line of claim 17 inwhich the lens is a magnetic quadrupole triplet focusing lens.
 19. Theion implanter beam line of claim 17 constructed to produce a beam havingan elongated cross-section profile entering the quadrupole tripletfocusing lens, with the long dimension of the beam profile in the planenormal to the plane of the bend of the analyzer magnet, in combinationwith a control adapted to cause the first lens element of the triplet tocause focusing in the long profile dimension, the second lens element tohave polarity opposite to that of the first element to cause focusing inthe short dimension and defocusing in the long dimension, and the thirdlens element to have the same polarity as the first element, fieldstrengths of the lens elements controlled, respectively, to achievesimultaneous focusing in both dimensions of the elongated profile. 20.The ion implanter beam line of claim 13 including a decelerating unitfollowing the analyzer magnet and preceding the quadrupole lens, thelens controlled to control beam divergence resulting from decelerationof the beam at the decelerating unit.
 21. The ion implanter beam line ofclaim 15 having beam line features and parameters of substantially thefollowing values; A. Analyzer Magnet: R=500 mm, φ=120°; G=118 mm; s₁=31mm; s₂=8.6 mm; h₁=8.7 mm; h₂=4.7 mm; W=166 mm; bending power=80 keVoctadecaborane. B. Mass selection aperture: about 8 mm minimum to about38 mm maximum. C. Quadrupole triplet focusing lens: aperture: 80diagonal between pole tips; pole tip field adjustable 0-5 kGauss. D.Beam Scanning Magnet; Vertical gap=80 mm; bending power=80 keVoctadecaborane. E. Collimator: Bending radius 900 mm; Pole gap=8 mm;bending power=80 keV octadecaborane and the total deflection introducedby the scanner and collimator combination being about 30°.
 22. An ionimplanter beam line configuration constructed for enabling implantationof cluster ions of multiple masses near a peak of interest, the beamline configuration comprising a mass analyzer magnet followed by amagnetic scanner and magnetic collimator combination that introducebends to the beam path, the mass analyzer magnet defining a pole gapbetween ferromagnetic poles of the magnet and a mass selection aperture,the pole gap sized to accept an ion beam from a low density ion sourcethat produces the cluster ions, the mass selection aperture capable ofbeing set to a mass-selection width sized to select a beam of thecluster ions of the same dopant species but incrementally differingmolecular weights, the ion implanter beam line including a multi-elementfocusing system in the portion of the beam line following the analyzermagnet which comprises multiple quadrupole focusing elements, theindividual field strengths of the lens elements of the lens systemadjusted to control the dimensions of the beam in orthogonal directionsof the beam cross-section and to simultaneously and substantially removeangular deviation at the target substrate that otherwise would occur asa result of the range of different masses of the cluster ions in the ionbeam the magnetic scanner and magnetic collimator being constructed tosuccessively bend the ion beam in the same sense, which is in theopposite sense to that of the bend introduced by the analyzer magnet ofthe beam line.
 23. The ion implanter beam line of claim 22 in which thelens system has at least three quadrupole elements and is constructed tosimultaneously control the dimensions and angular divergence of the beamin orthogonal directions of the beam cross-section by quadrupole fields.24. The ion implanter beam line of claim 22 in which the lens system isa quadrupole triplet focusing lens.
 25. The ion implanter beam line ofclaim 40 in which the lens is a magnetic quadrupole triplet focusinglens.
 26. The ion implanter beam line of claim 24 constructed to producea beam with an elongated cross-section profile entering the quadrupoletriplet focusing lens, with the long dimension of the beam profile inthe plane normal to the plane of the bend of the analyzer magnet, incombination with a control adapted to cause the first lens element ofthe triplet to cause focusing in the long profile dimension, the secondlens element to have polarity opposite to that of the first element tocause focusing in the short dimension and defocusing in the longdimension, and the third lens element to have the same polarity as thefirst element, field strengths of the lens elements controlled,respectively, to achieve simultaneous focusing in both dimensions of theelongated profile.
 27. The ion implanter beam line of claim 24, 25 or 26in which adjustable extraction optics associated with an ion source areconstructed to produce a degree of beam convergence in thenon-dispersive plane of the analyzer magnet and is optimized to size thebeam to be accepted at the entrance to the quadrupole over a wide rangeof beam currents from a few microamps to a few milliamps, and a widerange of energies, from about 4 keV to 80 keV, the quadrupole tripletproviding final optimization of the beam size and angular divergence atthe wafer or substrate in both the non-dispersive (vertical) anddispersive (horizontal) planes at the wafer or substrate includingcompensating for variations in beam size and angle introduced by theextraction optics over the range of energies and currents.
 28. The ionimplanter beam line of claim 22 including a decelerating unit followingthe analyzer magnet and preceding the quadrupole lens system in the formof a quadrupole triplet lens, the quadrupole lens system controlled tocontrol beam divergence resulting from deceleration of the beam at thedecelerating unit.
 29. An ion implantation beam line for use with an ionsource, the beam line comprising a mass analyzer magnet followed by amagnet scanner and magnetic collimator combination that introduce bendsto the beam path, the analyzer magnet for an ion implanter beam linecomprising a sector magnet having a center path radius of about 500 mm,a sector angle of about 120° and a pole gap of at least about 80 mm, themagnet associated with a single pair of coils, the magnet havingentrance and exit pole faces perpendicular to the axis of the ion beampath entering and leaving the pole gap, the analyzer magnet havingsubstantially no focusing effect upon the beam in the planeperpendicular to the plane of bend of the sector magnet, the magneticscanner and magnetic collimator being constructed to successively bendthe ion beam in the same sense, which is in the opposite sense to thatof the bend introduced by the analyzer magnet of the beam line.
 30. Theion implantation beam of claim 29 in combination with an ion focusingsystem preceding the magnet providing beam focusing in the planeperpendicular to the mass-dispersive plane of the magnet.
 31. The ionimplantation beam of claim 29 in which the focusing system compriseslens elements of an ion extraction system associated with the ionsource.
 32. The ion implantation beam claim 29 in which the pole gap ofthe analyzer magnet is substantially wider than the correspondingdimension of the maximum size ion beam it is constructed to pass, therebeing a lining of graphite or silicon between faces of the poles and thebeam path.
 33. The ion implantation beam of claim 29 in which polemembers defining the pole gap have pole faces shaped with trenches andshims that respectively lower and raise the pole surfaces toward themedian plane of the beam path to shape the magnetic field in mannerenabling use of relatively small pole width in relation to the pole gapdimension.
 34. The ion implantation beam of claim 29 in which polemembers defining the pole gap are embedded in and sealed to the wall ofa vacuum housing of nonmagnetic material through which the ion beampasses while subjected to the magnetic field of the analyzer magnet, andferromagnetic structure of the magnet between the pole members beinglocated outside of the vacuum housing.
 35. The ion implantation beam ofclaim 29 in which the analyzer magnet is a sector magnet constructed toproduce an adjustable magnetic field in the pole gap including a fieldexceeding about 10 kGauss.
 36. The ion implantation beam of claim 29 inwhich the analyzer magnet is constructed to analyze a beam extractedfrom a slot-form ion source extraction aperture of at least 12 mm widthand 90 mm height.
 37. The ion implanter beam line of any of theforegoing claims having an ion source capable of ionizing a material toproduce cluster ions by electron impact, the implanter having, within avacuum housing, a beam scanner and collimator following the massanalyzer magnet, and a system for admitting a gas, capable of formingnegative ions by interaction with the cluster ion beam, into a region ofthe vacuum housing of the scanner or collimator to provide neutralizingnegative ions to the beam.
 38. An ion implanter beam line combined withan ion source capable of ionizing a material to produce cluster ions byelectron-impact ionization, the beam line comprising, within associatedvacuum housing portions and preceding an implant station, an extractionelectrode assembly capable of extracting ions from the ion source toform a cluster ion beam, a mass analyzer magnet for the beam, and an ionbeam scanner and an ion beam collimator through which the analyzed beampasses, combined with a system for providing, downstream of the analyzermagnet, gas capable of forming negative ions by interaction with thecluster ion beam to provide neutralizing negative ions to the beam. 39.An ion implanter beam line combined with an ion source capable ofionizing a material to produce ions of a species suitable forimplanting, the beam line comprising, within associated vacuum housingportions and preceding an implant station, an extraction electrodeassembly capable of extracting ions from the ion source to form a beamof ions of the species, a mass analyzer magnet for the beam, and an ionbeam scanner and an ion beam collimator through which the analyzed beampasses, combined with a system for providing, downstream of the analyzermagnet, gas capable of forming negative ions by interaction with the ionbeam to provide neutralizing negative ions to the beam.
 40. The ionimplanter beam line of claim 11, 37, 38 or 39 in which the gas is SF₆.41. The ion implanter beam line of claim 40 in which the SF₆.gas isprovided at pressure between about 5×10⁷ to 10⁻⁵ torr.
 42. The ionimplanter beam line of any of the claims 11, and 37 to 41 in which thereis post accelerator structure beyond the magnetic analyzer that can postdecelerate the ions from the source extraction energy to a lower energy.